As disclosed in German patent application DE 10 2008 020 299 A1, a packaging machine includes two rolls having film material wound thereon. One of the two rolls is always a stock roll providing film material for the packaging process for the articles to be packaged if the film material wound on the active roll runs out. For reasons of environmental protection and cost, it is necessary to use the film material on the active roll until it has been unwound as far as possible down to the core. The end of the film on the active roll must be indicated so that the second roll (spare roll) can be brought into the packaging process to thus provide the film material wound thereupon to the packaging process.
As may be seen in the corporate brochure of the company Krones AG regarding the fully automated “Vario Pack Pro” packaging machine, there is disclosed a packaging machine for a wide range of applications. The bottles entering the packaging machine are separated into groups. The films used for wrapping each group are pulled off an active roll. The groups are then wrapped with the film and subsequently pass through a shrink tunnel. The individually cut film portions are separated from the film material pulled off the roll by means of a cutting knife according to the length required for wrapping the objects. The second roll, which is also associated to the packaging machine, is introduced to the packaging process when the film wound upon the first roll is running out.
German published application DE 40 21 402 A1 describes a device for monitoring rolls being depleted. This device is mainly used in wrapping machines for articles. The corresponding monitoring device essentially consists of detection means operating in the area of a supply station of the belt at a wrapping station and/or near a group of roll and support shaft arranged in the area of the station. These detection means allow detecting a predetermined value of electrical impedance generated by the group of roll and/or support shaft and/or determining functions of at least one radial dimension of the group of roll and support shaft. For this purpose, the means rests on the roll and moves in the direction of the core and/or the axis of the roll as the thickness of the film material wound on the roll decreases to thus use the measured signals for concluding the amount of film material still wound on the roll.
German published application DE 195 43 246 discloses a device for controlling rolls for wrapping machines. The web material (film material) is wound on a roll for the wrapping machines. The roll has a corresponding core around which the film material is wound. The roll rotates around its own axis of rotation to thus provide the film material wound thereupon to the wrapping machine. An optoelectronic and light-sensitive sensor is associated with the roll and is movable along an essentially radial direction of the roll itself during the unwinding process of the roll. The sensor allows determining the value of a chromatic property of an area of the roll and sending a signal of a hue to the sampling device, which corresponds to a preset sample value. The film material wound directly around the core of the roll is colored so that the sensor will sense another color value of the film when approaching the end of the film material on the roll and will thus indicate the end of the film material on the respective active roll.
U.S. patent application 2008/0142631 A1 discloses a system and a method indicating the supply of paper in a printer. The paper is wound around a core of a roll. The core has a predetermined diameter. The paper wound around the core reduces the diameter when the paper is used by the printer. A scanning means is provided, which determines the core diameter and the paper diameter. A signal is output when the length of the paper material wound around the core under-runs a certain threshold.
European patent application EP 2 093 172 A2 describes a paper supply for a printer, wherein the paper supply is arranged on at least one roll. The paper supply includes at least two receptacles for the rolls that are arranged in different ways so that different sizes of paper rolls may be processed by the printer. An adjustable end sensor is provided for detecting the end of the paper wound upon a core. The adjustability allows adjusting the sensor to the respective position of the roll.
Japanese patent application JP 600 12 449 A describes a device for detecting the end of a film material wound on a roll. For this purpose, a magnetic strip is provided across the width of the film material near the end of the film material. When the film material is unwound from the roll, this magnetic strip is detected by means of a detector, which indicates the end of the film material on the roll.
Furthermore, Japanese patent application JP 61 08 63 55 A describes an arrangement that allows detecting a joint and/or end of long film-like material. The joint runs transversely across the film web and is detected by means of two photosensors. The photosensors are arranged in the direction of transport of the film material.
German published application DE 44 42 154 describes a method for initiating an early change of rolls. For this purpose, contactless temperature measurement is provided at the front side. Based on the measured temperature near the core of the roll, the amount of paper still on the roll or already wound onto the roll may be concluded.
European patent application EP 0 730 960 A2 describes a method and a device for determining the end of film material wound on a roll. For this purpose, at least two strips that are detected by a corresponding sensor means are provided transversely across the film material on the film material. In one embodiment, the sensor means consists of a light source and a correspondingly associated photodetector. The strips indicating the amount of film material still wound upon the core are detected by the sensor means.
German published application DE 198 47 466 A1 describes a method and a device for detecting defective regions in unwindable plastic webs. The sensor is attached to a lever arm moving in the direction of the core depending on the film material unwound from the roll. The sensor detects marking elements applied to the film material that project laterally from the front side of the film material.